Last year’s forest fires in Indonesia caused the outbreak of a toxic haze across Southeast Asia that may have caused the death of at least 100,000 people in the region, a new study has found.

The study, conducted by researchers from Harvard and Columbia universities in the US, said the “killer haze” that choked the region between July and October has very likely caused more than 90,000 premature deaths in Indonesia.

The research published in Environmental Research Letters on Monday also estimated several thousand more deaths in neighboring Singapore and Malaysia.

The study focused on the impact of the haze on adult deaths. It said early deaths were mainly caused by cardiovascular disease and respiratory illnesses.

The researchers are now working on a further study to examine the impact of the 2015 haze on children.

The air pollution may have caused an increase in child deaths from pneumonia in Indonesia, according to Sam Myers, one of the study’s authors.

People wait at a health center following thick haze in Indonesia’s Riau province on September 14, 2015. (Photo by AFP)

A Greenpeace campaigner in Indonesia warned that “this killer haze will carry on taking a terrible toll, year after year,” unless the authorities take action to resolve the crisis.

“Failure to act immediately to stem the loss of life would be a crime,” said Yuyun Indradi.

The figure revealed by the study is far higher than the previous official death toll that was given by Indonesian authorities of only 19 deaths in the country.

According to the study, there were 91,600 deaths in Indonesia, 6,500 in Malaysia and 2,200 in Singapore.

Indonesia’s last year blaze that continued for weeks was caused by fires set in forest and on carbon-rich peatland to quickly and cheaply clear land for palm oil and pulpwood plantations.